German DE-AS 24 01 090 discloses a method for manufacturing steel from fine-grained iron ores. In that method, the preheated and partially reduced iron ore is reduced to iron sponge in a counter-flow current with gases consisting almost exclusively of carbon monoxide in a vortex reactor at 500 to 850.degree. C. The iron sponge is delivered pneumatically from the vortex reactor to a smelting furnace in such a way that it is charged into the iron smelt with a multiple jet cap arranged below the surface of the bath.
Three reactors are required to carry out this method. One is for pre-reduction, one for reduction (in the vortex process), as well as one for smelting. This procedure entails problems, particularly the problem of transporting the prereduced material, which has a tendency to reoxidize, as well as the risk of collapse during the direct reduction.
The present invention decreases the number of steps required in the process for direct manufacture of steel from iron ore dust by direct reduction. Furthermore, the disturbances occurring presently caused particularly by the reoxidation of the prereduced material and/or by collapsing of the material during the direct reduction, are eliminated. Another achievement of the invention is the reduction of the number of installation parts, and the simplification of transport between the individual installation parts. This is solved by the method for manufacturing steel from iron ore dust by direct reduction, whereby the iron ore dust is preheated, then reduced with a gas mixture containing monoxide and the reduction product is charged into an iron smelt below the surface of the bath, distinguished in that the iron dust is introduced into a reducing gas in a continuous current, which is preheated to about 400.degree. to 800.degree. C., containing predominantly H.sub.2 and at the same time serving as adjuvant, and immediately upon this introduction it is delivered through a reduction duct going almost to the bottom of a smelting aggregate, whose interior is heated to 1,000.degree. to 1,400.degree. C., after which the metallic iron spontaneously reduced from the iron ore dust, following the delivery of the adjuvant gas current and the free fall, is transformed to the molten state in the iron smelt present in the smelting vessel. Advantageous further developments of the invention are contained in the dependent claims.
In the method of the invention, a gas mixture of about 300.degree. C. and rich in H.sub.2 is heated, recuperatively, from the waste or exhaust gases of an iron smelting aggregate to about 700.degree. C., and fed to a reducing duct. Immediately before admitting the gas mixture into the upper portion of this reducing duct arranged in the furnace chamber of an iron smelting aggregate, microfine ground ore is added to the gas current. In the reaction duct, the lower end of which is immersed in a molten Fe metal bath, the solid-gas-mixture is heated to about 1,200.degree. C. so that it is practically spontaneously reduced from reduction gas to metallic iron. Subsequently, the iron, following the gas current and/or the free fall, is pressed into the molten phase together with the gas mixture, where it is transformed into the molten state.
The metal bath is supplied with energy in order to avoid cooling of the molten iron by the solid-gas-mixture entering the molten phase, where the temperature is below the liquidus temperature of the iron. Furthermore, it is supplied to compensate for the temperature loss of possibly occurring tail reactions of the endothermal reduction processes taking place via hydrogen, and finally to compensate for the radiation losses of the smelt bath.
The waste gas emerging from the metal bath, consisting of the components H.sub.2, CO, H.sub.2 O, CO.sub.2, is immediately upon issuing from the smelting aggregate, fed to the reducing gas for recuperative heat exchange. Following that the waste gas is dried and, as a rule, fed again directly to the process. In order to balance the loss of the gas components oxidized by the reducing process, the process is to be supplied at all times with fresh, live gas, which may, for example, be supplied from natural gas and water vapor in a gas transformer. The mixed gas is mixed with the reconditioned gas from the process, recuperatively heated, mixed with iron ore dust, and fed to the reduction duct.
For this method of the invention, the usual safety measures for preventing explosions must, of course, be taken, which are required for processes where a reducing gas containing H.sub.2 is used. Above all, all parts of the installation must be gas proof.
The method of the invention is distinguished by the fact that steel is manufactured from ore in one step, whereby the reducing potential of hydrogen, which is favorable for high temperatures, is utilized. There is almost no metallurgic work done in the smelting aggregate. Only a separation of the metallic iron from the oxidic matrix takes place here. The smelting aggregate is provided with two tap holes, which are located in the usual manner at different levels in order to tap metal and slag separately. Also, the method of the invention makes it possible to reduce the number of the usual steps in the process, the transport distances between the individual parts of the installation are thus shortened.